Method of cooling bulk material



1952 s. PETERSEN METHOD OF COOLING BULK MATERIAL 2 SHEETS-SHEET 1 FiledNov. 25, 1950 I VENTOR BY ki %M5%% M ATTORNEYS Feb. 26, 1952 s. PETERSENMETHOD OF COOLING BULK MATERIAL 2 SHEETSSHEET 2 Filed Nov. 25, 1950 ATTOR N EY5 Patented Feb. 26, 1952 METHOD OF COOLING BULK MATERIAL LouisSteflen Petersen, Forest Hills, N. Y., as-

signor to F.-L. Smidth & 00., New York, N. Y., a corporation ofNewJersey Application November'25, 1950, Serial No. 197,563 InDenmarkDecember 30, 1949 '5 Claims.

1 This invention relates to the cooling of bulk material discharged froma kiln after having been burned therein by combustion of a fuel-airmixture, examples of such materials being cement clinker, burnt lime,roasted .iron ore, aluminum oxide, etc. More particularly, the inventionis concerned with a novel method of cooling bulk materials by means ofair in an .efilcientmanner and utilizing the heated cooling air in thecombustion of the fuel in the kiln.

Air coolers for cooling bulk material discharged from a kiln afterhaving been burned therein are well known and, in such coolers, thetemperature of the material is reduced to the desired degree, before thematerial is passed to storage or subjected to further treatment, andheat is recovered by the heating of the cooling air. The heated coolingair may then be used as preliminary or secondary air for the combustionof the fuel in the kiln, although usually the amount of air employed forcooling the material is greater than that required for combustionpurposes. Accordingly, some of the air used for cooling has heretoforebeen allowed to escape to the atmosphere, with the result that heat islost and dust entrained in the air is discharged into the atmosphere.

The present invention is directed to the provision of a method ofcooling which overcomes the disadvantages of the prior methods and, inthe practice of the new method, the cooling is effected in two stagesand in such manner that at least part of the air is employed in bothstages and then utilized as secondary air in the kiln. The remainder ofthe cooling air, if any, which was utilized in the low temperature stageof the cooling, may then by-pass the high temperature stage and beintroduced into the kiln either as primary or secondary air.

jAir coolers, in which two stage cooling is employed, have been usedheretofore but. i Such coolers, the air currents pass through the twostages of the cooler in parallel, so that cold air isused in each stage.The air, which cools the material in the high temperature stage adjacentthe kiln, is then introduced into the kiln ordinarily as secondary air,while the air employed in thelow temperature stage is usually discharg dinto the atmosphere. In the practice of the method of the invention, theair employed in the high temperature cooling has been used in the lowtemperature stage and all of the air employed in the low temperaturestage may be used in the high temperature cooling or part-of this airmaybe withdrawn and employed as either preliminary or secondary air ofcombustion. While the cooling action in thehigh temperature stage issomewhat less than thatoccurring in the prior coolers, in which cold airis employed in both stages, it has been found in practice that a highlyeflicient cooling action is obtained in the practice of the new method.

In cooling bulk material in accordance with the method, the material isadvanced in a thin layer from the exit end of the kiln to a deliverypoint and air is passed in contact with the material in a part ofthelayer remote from the kiln to effect finalcooling of the material andpreliminaryheating of the air. At least part of the heated air is thenpassed in contact with the material in the part of the layer adjacentthe kiln to efiect preliminary cooling of the material and final heatingof the air. The finally heated air is then introduced into the kiln toserve as secondary air for combustion. It, in the practice of themethod, all of the air employed in the low temperature cooling stage isalso used in the high temperature stage, all of the heated cooling airis employed as secondaryair in the kiln. .If desired, however, part ofthe air used in the low temperature may be employed in the kiln, eitheras primary or secondary air and the remainder may be used in the hightemperature stage.

In carrying out the method, the material may 1 be advanced from the exitend of the kiln to the delivery point by means of an endless conveyorWithin a chamber connected to the kiln hood and having aninlet for airand an outlet for material. The space within the chamber above theconveyor is subdivided by a partition and air entering the inlet flowsdown through the material and conveyor at one side of the partition and,at the other side, flows up through the conveyor and material. Theheated air then passes through the hood into the kiln to serve assecondary air stretches movingi-n opposite directions. The materi'aldischarged from the kiln 'is'deposited upon 3 one stretch of theconveyor and passes therefrom to the second stretch, which delivers thematerial to the point of discharge. The low temperature stage of coolingis effected by passing air through the second stretch of the conveyorand the material thereon and the high temperature cooling,

is effected by passing all or part of the air utilized in the lowtemperature stage through the first stretch of the conveyor and thematerial thereon.

Instead of using a conveyor in the practice of the method, the kiln maybe equipped with an extension receiving the burned material from the hotzone and provided with grates, through which cooling air may flow topass through the material traveling down the kiln extension. Thematerial passes from the extension into cooling tubes mounted on theextension and lying lengthwise of the kiln. The material forms a thinlayer in both the extension and the tubes and the low temperaturecooling is effected by air drawn through the tubes counter-current tothe material and entering the kiln extension. Part of the air enteringthe extension from the tubes passes upward through the extension intothe kiln to' serve as secondary air of combustion, while the remainderof the air is withdrawn from the extension and then returned beneath thgrates in the extension, so as to flow upward through the layer ofmaterial on the grates and effect the high temperature cooling. The airused in the high temperature stage passes from the extension into thekiln to serve as secondary air.

For a better understanding of the invention, reference may be made tothe accompanying drawings, in which:

Fig. 1 is a longitudinal vertical section through one form of apparatusfor practicing the new method;

Fig. 2 is a view, partly in elevation and partly in longitudinalvertical section, of another form of such apparatus;

Fig. 3 is a view, partly in elevation and partly in longitudinalvertical section, of a third form of such apparatus on the line 3-3 ofFig. 4; and

Fig. 4 is a sectional View on the line 4-4 of Fig. 3.

The apparatus shown in Fig. 1 includes a chamber I connected to thelower end of the hood into which projects the discharge end of a rotarykiln l2. A fuel-air mixture is introduced into the kiln through a burnerpipe l3 projecting through the hood and into the kiln and the hotproduct of the kiln falls upon the upper stretch of a gas-permeableconveyor M, such as a chain grate, within the chamber. The con-- veyoris trained about drums l5, l6 and drum l6 lies close to an outlet l1,through which the material discharged from the conveyor may leave thechamber. The chamber is provided with an air inlet H3 at its top abovethe discharge end of the conveyor and the space within the chamber abovethe conveyor is subdivided by a transverse partition |9, which dependsfrom the top of the chamber and has a flexible lower end section |9alying in contact with the layer 20 of material on the conveyor.

In the operation of the apparatus shown in,

Fig. l, cooling air introduced through inlet I8 passes down through thelayer of material and the conveyor at the right of partition H) toeffect low temperature cooling of the material and preliminary heatingof the air. The air then flows beneath the upper stretch of the conveyorpast partition I9 and flows upwardly through the conveyor and materialand through the hood out through discharge 42.

into the kiln to serve as secondary air. All of the air heated in thefinal cooling of the material is used for cooling the material in thehigh temperature cooling stage and all of the air thus heated in the twostages is used for secondary air of combustion in the kiln.

The installation illustrated in Fig. 2 comprises a chamber 2| having aninlet 22 for material, which is connected by a clinker chute 23 to thebottom of the head 24 of a rotary kiln 25. A fuelgas mixture is suppliedto the kiln through a burner pipe 26extending through the hood and intothe kiln. A platform 21 is mounted on the wall of the chamber belowinlet 22, so that clinker discharged from the kiln and landing on theplatform forms apile 28 having a sloping surface, down which additionalmaterial moves.

An endless conveyor 29 is trained about rotary drums 30, 3| within thechamber and the upper stretch of the conveyor passes along the uppersurface of gas-permeable support 32 forming the top of a wind box 33mounted in the chamber between the two stretches of the conveyor andhaving an inlet 34. Theconveyor is of the chain type and the links aresufficiently spaced to permit large pieces of the material to passbetween them. As the material flows from pile 28 on platform 21, itforms a layer 35 advanced over the top of support 32 by the conveyor. Aplate 36 is mounted beneath the upper stretch of the conveyor at the endof support 32, toward which the material is advanced, and, when thematerial is moved over the plate, it drops between the links of theconveyor.

The lower part of the housing below the lower stretch of the conveyorforms a second wind box 31 having a gas-permeable support 38 at its topand an air inlet 39. The material passing through the links of the upperstretch of the .conveyor and dropping from plate 36 falls upon a plate40. which is an extension of the perforated support 38, and the materialis then advanced by the lower stretch of the conveyor along plat 40 andsupport 38. When the material reaches the end of wind box 31, it dropsbetween the links of the conveyor and enters hopper 4| having an outlet42.

The chamber is provided beneath drum 3%! with a hopper G3 to collectlarge pieces of the material, which have not fallen through the upperstretch of the conveyor. Hopper &3 is normally closed and is opened fromtime to time for discharge of the material collected therein.

The chamber 2| is provided at its top above hopper 4| with an air outlet44 connected by a duct 45 to a dust separator 46. Solid particlescollected in the separator return through duct 41 to, chamber 2| anddrop into hopper 4| to flow The air leaving the separator 46 isconducted by duct 48 to the intake of a fan 49 and the outlet of the fanis connected by a duct 50 to the inlet 34 of wind box 33. A branch duct5| containing a damper 52 leads from duct 48 to burner pipe 26, so thatpart of the air issuing through outlet 54 from the chamber may besupplied to the burner pipe to form part of the primary air ofcombustion.

A fan 53 supplies air through a duct 54 to the inlet 39 of wind box 37.The air escaping upwardly through support 33, the lower stretch of theconveyor, and the layer of material thereon,

is prevented from flowing into the space above the upper stretch of theconveyor by a flexible partition means 55 mounted on wind box 33 and 5,bearing on the layer of material on the lower stretch of the conveyor.

In the Operation of the installation described, the hot product of thekiln .falling through chute 23 and entering chamber 2! through inlet 22deposited to form layer 35 on the support 32. The material is advancedalong the support by the upper stretch of the conveyor and,'.during itsadvance, the material is cooled .by air issuing from wind'box 33 throughmaterial inlet 22 and passes' up the clinker chute 29 and through bond24 to enter the kiln, where it serves as secondary air of combustion.The materiel falling off plate 35 to the lower stretch of the conveyoris advanced over plate 40 and permeable support 38 to be discharged intohopper il. In its advance over support 38 by the lower stretch of theconveyor, the material is cooled by air escaping from wind box 31. Theair, which has been passed through the material being advanced by thelower stretch of the conveyor, is freed of dust in separator 46 and apart of the air determined by the setting of damper 52 passes to theburner pipe and serves as primary air of combustion. The remainder ofthe air from the separator is delivered by fan 49 into wind box 33 foruse in the high temperature stage of cooling of the material on theupper stretch of the conveyor, and then flows up into the kiln, asdescribed.

In the installation described. it will be noted that all of the air,which has been preliminarily heated in the low temperature stage ofcooling of the material on the lower stretch of the conveyor, may beemployed in the high temperature stage and then used as secondary air ofcoinbustion. Instead, part of the air heated in the low temperaturecooling stage may be used as primary air and the remainder in the hightemperature stage. All of the air employed in the high temperaturestageis air, which has been heated in the low temperature stage, and allof the air used for high temperature cooling is supplied to the kiln assecondary air.

The apparatus illustrated in Figs. 3 and 4 comprises a rotary kiln 56having an extension 58 provided with grates 59 mounted on supports 60attached to the inner surface of the extension. Longitudinal passages 9!lead from the lower end of the extension to the space beneath the gratesand, beyond the grates, the extension is provided with outlets 62leading to conventional cooling tubes 53 mounted lengthwise of theextension on the outside thereof, the tubes being open at their upperends and containing means for advancing material through them, as thekiln rotates.

A stationary casing 64 is mounted at the lower end of the extension 58and the casing has an air inlet opening 65 in its wall at the end of theextension. A burner pipe 55, for supplying a fuel-air mixture to thekiln, projects through casing 64 and into the extension. The casing 64has an air outlet 61 connected to the inlet of a fan (not shown) and theoutlet of the fan is connected to the inlet 58 of a stationary casing 69mounted beneath casing 66 and having outlets 19 aligned with the ends ofpassages 6| at the lower part of extension 58.

In the operation of the apparatus shown in Figs. 3 and 4, the hotproduct of the kiln travels down through the extension to form a thinlayer "H overlying the grates 59 at the lower side of the extension. Thematerial issues through outlets 62 and enters the cooling tubes 63, upwhich the material is conveyed in thin layers by the usual means toescape-at the upper ends .of the tubes. At its upper end, the kiln isconnected with a chimney and, if necessary, also with-a fan, so thatthere is reduced pressure in the extension. Air is, accordingly, drawnthrough the cooling tubes into the extension and, as the'air flowscountercurrent to the thin layers of material in the tubes, the airefiects-the low temperature stage of cooling and is preliminarilyheated. Some of the air thusheated is drawnupward through the extensioninto thekiln-to-serve as secondary air of combustion. The remainder, ofthe air heated in the low temperature cooling'stage is drawn into casing64 by the fan connected to the casing outlet and. all or *partof the airdrawn from casing 64 isreturned to casing GQ -and fiows through passages61 into the spaces beneath grates 59 at the lowerpart of the extension.The air escaping upwardly between the grates and through the layer Y Hof material effects the high temperature stage of cooling of thematerial. The air heated in the high temperature cooling stage thenflows through the extension into the kiln to serve as secondary air forcombustion.

With the arrangement described, all of the air used in the hightemperature cooling stage is air, which has been employed in the lowtemperature stage. Some of the air heated in the low temperature stagepasses directly to the kiln to serve as secondary air and the remainder,or a part thereof, is then used in the high temperature stage. Ifdesired, the air drawn from casing 64 may pass through a cycloneseparator similar to separator 46 before passing to the fan and beingreturned to casing 69.

Reference is made to applicants co-pending application Serial No.197,564, filed November 25, 1950, Apparatus for Treating Bulk Material,which relates to an apparatus, which may be used in the practice of themethod of the present application.

I claim:

1. The method of burning and cooling bulk material which comprisesburning the material in a kiln by combustion of a fuel-air mixture untilthe material has been burned to the desired extent, then discharging thematerial from the kiln, forming the discharged material into anelongated bed, advancing the bed of material as a thin layer from theexit end of the kiln to a delivery point, passing air transversely andcompletely through a part of the bed remote from the kiln to effectfinal cooling of the material and preliminary heating of the air,preliminarily reducing the temperature of the material by passing atleast part of the heated air transversely and completely through a partof the bed adjacent the kiln, said preliminary reduction of thetemperature of the material resulting in a final heating of the air, andintroducing the finally heated air into the kiln to serve as secondaryair of combustion during the burning of the material.

2. The method of claim 1 in which a part of the air which was passedthrough the material to efiect final cooling of the material is suppliedto the kiln and used therein as primary air for the burning of thematerial in the kiln.

3. The method of claim 2 in which the air which was passed through thematerial to efiect final cooling thereof is subjected to a separationoperation to remove entrained solids therefrom.

4. The method of claim 1 in which a part of the air which was passedthrough the material to effect final cooling of the material isseparated from the remainder thereof before any part of the remainderthereof ispassed through the bed of material adjacent the kiln to effectpreliminary reduction of the temperature of the mate rial and issupplied to the kiln and used therein ail primar air for'the burning ofmaterial in the k n.

5. The method of claim 1 in which the bed 0 material is advanced as athin layer in successive stages, the air is passed through the layer inthe second stage remote from the kiln to efiect the final c001ing of thematerial, and at least a part of the resulting heated air is thereafterpassed through the first stage adjacent the kiln to effect thepreliminary reduction of the tem- 15 perature of the material.

8 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Bauer Nov. 'I, 1950

